I got it apart last night and think I might have figured it out. This little spring detent on the hammer was stuck and wouldn't spring in/out. I put some kroil in there and worked it back and forth until it was free, and then reassembled. I can draw the hammer back now and the cylinder rotates as it should, but now the loading gate is stiffer to open, and the cylinder doesn't rotate with it open. I'm thinking it has something to do with the loading gate spring.

Sorry I did not find this thread sooner but I'm sure you found the primary problem.
And I think you are looking in the right direction on the follow up problem.
The loading gate spring is easy to dislodge when cycling and or dry firing with the cylinder out . Sometimes, if the tip has been polished ,dry fire with no cartridges or snap caps will let it happen.
Usually no disassembly required other than cylinder removal. Easily seen in your first picture you can see the tip under the loading gate. If it is sticking out , it is wrong. Hold the loading gate closed and just push it down and in. Should pop into place. If that does not work remove the two back screws and loosen the three bottom screws. Pulling the gripframe down a little can relieve pressure on the loading gate spring. IF THE GRIPFRAME MOVES, don't force it. If it doesn't you may have to remove the gripframe and re assemble.

The unattached leg of the trigger return spring is very common and not an issue. Widely done it is known as a lazy, easy way to reduce trigger pull. There are much better ways to do this but it seems to be harmless ,,,,and easily reversible.
Too bad your not closer , we could get ya fixed up in a heartbeat, but it seems your getting there just fine.

The loading gate spring is easy to dislodge when cycling and or dry firing with the cylinder out . Sometimes, if the tip has been polished ,dry fire with no cartridges or snap caps will let it happen.
Usually no disassembly required other than cylinder removal. Easily seen in your first picture you can see the tip under the loading gate. If it is sticking out , it is wrong. Hold the loading gate closed and just push it down and in. Should pop into place.

Yep, that was the problem; glad it was a (relatively) easy fix! On the plus side, I'm not too shabby at disassembly/reassembly with these now It was a bit of a headache the first few times...

As Shooter444 said, the single leg spring is an old trick to lighten the trigger pull. I'd put it back where it belongs and see if that fixes your problem.
The cylinder stop that you pointed to is supposed to lock up when hammer is cocked to keep the cyl aligned with the bore and from moving allowing the lead to hit the frame from misalignment- it locks into the cyl notches. It should be down at other times to allow the cyl to move freely. It may not act the same with the cyl open as when loading.

eta- oops- didn't finish reading page 2... glad you found the problem and are able to fix it- now go shoot'in